Particularly in veterinary applications, syringes are known which allow a syringe barrel to be filled repeatedly from a fluid container and to discharge the drawn fluid manually from the syringe barrel. This allows repeated injections of a precisely predetermined volume, as in the case of, for example, serial vaccinations or treatments of animals, and does not require the cumbersome filling of the syringe from a separate fluid container. The prior art syringes comprise two check valves. A first check valve is located between the syringe barrel and the discharge outlet and is connected such that fluid flow is possible only from the syringe cylinder to the discharge outlet, but not a counterflow such as might occur when drawing fluid from the fluid container connected with the syringe. A second check valve allows a fluid flow from the fluid container to the syringe barrel when pulling back the plunger, but not when advancing the plunger.
Such valve system is known for different fluid container systems. In a first construction, a fluid container is attached directly to the syringe, so that stored fluid flows into the syringe barrel by advancing the plunger. For this purpose, the fluid container is provided with a suitable pressure compensation mechanism preventing a vacuum from being generated within the fluid container. In a second variant, the fluid is contained under pressure and, when suitably released, automatically flows into the syringe barrel while pushing back the plunger. It is known to conduct a stop detection in these types of pressurefillable syringes, so that, when the syringe has been emptied, i.e. when the plunger is maximally advanced into the syringe barrel, the syringe barrel is automatically refilled, pushing back the plunger.
In particular, in the aforementioned second type of syringes, which are filled via a fluid container connected therewith, there may occur, during a filling operation, an undesired discharge of fluid through the discharge outlet, which is generally caused by the response behavior of the two check valves.
Therefore, it is the object of the invention to improve a syringe of the aforementioned type such that undesired discharges of fluid no longer occur during filling of the syringe barrel.